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HelpTest Code THSCM Thyroid Function Cascade, Serum
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| STSHC | TSH, Sensitive, S | Yes, (order STSH) | Yes |
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| FRT4C | T4 (Thyroxine), Free, S | Yes, (order FRT4) | No |
| TPOC | Thyroperoxidase Ab, S | Yes, (order TPO) | No |
| T3C | T3 (Triiodothyronine), Total, S | Yes, (order T3) | No |
Testing Algorithm
If thyrotropin (TSH, formerly thyroid-stimulating hormone) is less than 0.3 mIU/L, then free T4 (thyroxine) is performed at an additional charge.
If FT4 is normal and the TSH is less than 0.1 mIU/L, then T3 (triiodothyronine) is performed at an additional charge.
If TSH is greater than 4.2 mIU/L, then free T4 and thyroperoxidase antibodies are performed at an additional charge.
For more information see Thyroid Function Ordering Algorithm.
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumSpecimen Required
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1.5 mL
Collection Instructions:
1. Serum gel tubes should be centrifuged within 2 hours of collection.
2. Red-top tubes should be centrifuged and the serum aliquoted into a plastic vial within 2 hours of collection.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 7 days |
| Frozen | 30 days | |
| Ambient | 72 hours |
Reference Values
0-5 days: 0.7-15.2 mIU/L
6 days-2 months: 0.7-11.0 mIU/L
3-11 months: 0.7-8.4 mIU/L
1-5 years: 0.7-6.0 mIU/L
6-10 years: 0.6-4.8 mIU/L
11-19 years: 0.5-4.3 mIU/L
≥20 years: 0.3-4.2 mIU/L
Day(s) Performed
Monday through Sunday
CPT Code Information
84443
84439 (if appropriate)
84480 (if appropriate)
86376 (if appropriate)
Clinical Information
This test utilizes a cascaded testing approach to efficiently evaluate and monitor functional thyroid status.
The cascade begins with thyrotropin (TSH, formerly thyroid-stimulating hormone) as a screening assay. In patients with an intact pituitary-thyroid axis, TSH provides a physiologic indicator of the functional level of thyroid hormone activity. Increased TSH indicates inadequate thyroid hormone, and suppressed TSH indicates excess thyroid hormone.
Transient TSH abnormalities may be found in seriously ill, hospitalized patients, so this is not the ideal setting to assess thyroid function. However, even in these patients, TSH works better than total T4 (thyroxine, an alternative screening test).
When TSH is normal, no additional testing will be necessary. However, when the TSH result is abnormal, appropriate follow-up tests will automatically be performed.
If TSH is below 0.3 mIU/L or above 4.2 mIU/L, free T4 is performed. The supplemental measurement of free T4 in patients with abnormal TSH measurements allows one to better assess the severity of the changes.
Serum T3 (triiodothyronine) levels often are depressed in sick and hospitalized patients, caused in part by the biochemical shift to the production of reverse T3. Therefore, T3 generally is not a reliable predictor of hypothyroidism. However, in a small subset of hyperthyroid patients, hyperthyroidism may be caused by overproduction of T3 (T3 toxicosis). To help diagnose and monitor this subgroup, T3 is measured on all specimens with suppressed TSH and normal free T4 concentrations.
Detectable concentrations of antithyroperoxidase (anti-TPO) antibodies are observed in patients with autoimmune thyroiditis and may cause the destruction of thyroid tissue, eventually resulting in hypothyroidism. Anti-TPO antibodies are measured in all specimens with elevated TSH concentrations.
For more information, see Thyroid Function Ordering Algorithm.
Report Available
1 to 2 daysReject Due To
| Gross hemolysis | Reject |
| Gross lipemia | OK |
| Gross icterus | OK |
Method Name
Electrochemiluminescent Immunoassay
Forms
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.